1. Field of the Invention
The present invention relates to information recording/replaying apparatus and method. In particular, the present invention is effective when recording broadcast content to a hard disk, and transferring the content recorded on the hard disk to other recording media. This serves to improve easy handling for users, while protecting the copyright of the broadcast content.
2. Description of the Related Art
As is well known, in broadcasting, content having copy-once copyright information (copy once: one-time copy is permissible) is used. Copy-once means that the content is permitted to be recorded to a recording medium by only one generation.
The content having copy-once copyright information is not permitted to be recorded on other media when it is received by an HDD (Hard Disk Drive) built-in receiver and recorded to a hard disk. In this case, the content recorded to the hard disk has copy-no-more copyright information (copy-no-more: copy is not permissible).
Incidentally, HDDs are easy to handle because the access speed is high; however, they have a limited recording capacity. In order to effectively use the limited recording capacity, the user has the following needs. That is, the user desires to transfer the content to be saved for a long period to individual media such as a DVHS (Digital Video Home System).
In order to meet the above user needs, the following function is considered. Under the condition that the content recorded to the hard disk is erased, the recorded content is replayed from the hard disk, and the replayed content is recorded to other media. This function is called “move”.
Content transfer from a hard disk to a DVHS is carried out in the following manner. Apparatuses first recording the content, that is, an HDD built-in receiver, temporarily reproduces the corresponding content from the hard disk, thereafter, records the replayed content to the recording media such as DVHS.
Incidentally, when the HDD built-in receiver records the content, in order to prevent illegal copy, the following processing is carried out in general. That is, the content is encrypted, thereafter, recorded to the hard disk.
For this reason, if the encrypted content is read from the hard disk and is recorded to the recording media by the DVHS, it is impossible to reproduce the content by the apparatus recording it.
Thus, when replaying the encrypted content from the hard disk, the content must be outputted to the DVHS after the cipher is decrypted. In this case, IEEE 1394 (Institute of Electrical and Electronics Engineers) is used as a read signal transmission line. Further, the content is protected using a protection mechanism such as DTCP (Digital Transmission Content Protection).
If the replaying work is interrupted during content transfer from the hard disk to the DVHS, the content portion already recorded to a recording medium by the DVHS must be erased from the hard disk. This is to prevent the content portion recorded to the recording medium from being again replayed and recorded to another recording medium.
In the broadcast technique, there is the case where the HDD built-in receiver records the content, thereafter; a content having a limitation in the number of replaying and seeing/hearing times is broadcasted. As described above, when the content has limitation in the number of replaying times, the HDD built-in receiver records and manages already replayed time condition information and replayable time condition information in the hard disk.
When the number of replayable times represented by the time condition information is one or more, the HDD built-in receiver makes a replaying limitation based on the above time condition information so that the content can be replayed.
In the broadcast technique, there is the case where copyright information is given to the broadcasted content. In this case, the HDD built-in receiver also records the copyright information to the hard disk.
In such a case, in order to prevent the copyright information from being altered, the following method has been proposed. That is, the copyright information is included as a cipher key for encrypting the corresponding content in an operation element generating the cipher key. According to the above method, if the recorded copyright information is altered, a decryption key for decoding the content is correctly found; therefore, it is possible to prevent illegal alteration of the copyright information.
The HDD has a function of backing up the content recorded to the hard disk in the HDD before transferring it, and restoring the backup data after transfer. As a result, it is difficult to securely erase the content and key information. In order to solve the problem of erasing the key information by the above backup restoration, there has been proposed a method of storing the key information outside of the HDD.
More specifically, in the conventional case, the whole contents are encrypted using one cipher key, and thereby, are protected. For this reason, when the content transfer is interrupted halfway, all the contents must be erased in order to make impossible the replay of the content portion already transferred.
In this case, however, there is a problem that the non-transfer portion of the content is neither replayed nor transferred later. The transfer interruption is probably caused not only user's will but also accidental power-off. In this case, necessary portions of the contents are lost regardless of the user's will.
In order to securely erase the content equivalent to already transferred portions from the hard disk using the conventional method, the following method is employed. For example, the cipher key of the content is changed in one-minute units, and then, the use of a key for the replayed portion is inhibited. However, according to the above method, 120 keys must be prepared for 120-minute content; for this reason, there is a problem that key data management is very difficult.
Further, there has been proposed the following method. That is, a key value changing every minute is set as a value obtained from only previous one-minute keys of the content by an operation, and only the key value just as transfer is completed is stored. By doing so, there is no need of acquiring keys relevant to the transferred content portions; therefore, the number of keys can be reduced.
This is a method that is effective in reducing the number of keys and preventing the transferred content from being again replayed. However, when making content random access replay, in order to calculate the key value at the replay start time, there is a need of calculating all keys every minute from the content start time to the replay start time. For this reason, when replaying the content while jumping it, there is a problem that this operation must be performed according to the distance from the header of the content to the replay start position thereof.
When the copyright information has a content replaying time limitation, the number of replaying times is updated every time the content is replayed. For this reason, according to the method of including the copyright information in the content cipher key, the content must be again encrypted upon every replay.
When the content replay is interrupted halfway, there is a problem that the number of replayable times from the content start time to the completion time reduces accordingly.